A system and method are disclosed for correcting distortion in medical images. Specifically, the subject matter relates to correction of distortion in magnetic resonance images (MRI) due to magnetic field variation.
Echo-planar imaging (EPI) is a fast magnetic resonance (MR) imaging technique that allows acquisition of single images in as little as 20 msec and of an entire image volume in as little as 0.5 seconds. Echo-planar imaging achieves its speed by obtaining all in-plane spatial-encoding information after a single radio-frequency (RF) excitation. EPI can be less sensitive to motion than conventional MR imaging and it allows imaging of rapidly changing physiologic processes such as blood flow and kinetic activity. EPI can be used to shorten scan time, providing new areas of MR imaging research and clinical applications. However, EPI is highly susceptible to image distortion, which results from especially to noises generated due to magnetic field variations and generates distorted images. Spatially varying local and main field inhomogeneity results in geometric distortions in the EPI image. Image voxels may be distorted through compression or stretching, depending on the local field gradients.
Some of the existing techniques measure distortion accurately, and other techniques acquire each data set twice in opposite directions to deduce the translation and intensity correction. Field mapping techniques, commonly used for distortion correction, acquires phase images and measures variations in the magnetic field to calculate local distortion correction pixel shifts in the image. These techniques require longer acquisition times, are susceptible to noise in the data and sometimes suffer from resolution limitations, especially at high fields.
Therefore, better techniques for correcting distortion of MRI image due to magnetic field variation are required.